Hi everybody !
First, I apologize for my poor english (it isn’t my first language).
I would like to move vertically (in oscillation) 20kg with 4 speakers in phase.
Frequency : between 20 and 200 Hz. Amplitude : less than 1 mm (50 microns).
My questions are :
- What power do I need ?
- What cheap amp and speakers can I buy ?
---
Some explanations :
I would like to move a giant mixture of non-newtonian fluid to make Faraday waves.
- This non-newtonian fluid is made of cornstarch and water (so, it is edible by children).
- Faraday waves are a very funny phenomenon. Here is a famous video about it ("fingers" start at 2:00) : http://www.youtube.com/watch?v=nq3ZjY0Uf-g
---
Every year, I build a machine for children. Last year, it was a vortex cannon called "boum".
(Examples : http://www.youtube.com/watch?v=lMLop6MIwUU)
If I succeed, the new machine will be called "life".
Thank you very much for your help !
First, I apologize for my poor english (it isn’t my first language).
I would like to move vertically (in oscillation) 20kg with 4 speakers in phase.
Frequency : between 20 and 200 Hz. Amplitude : less than 1 mm (50 microns).
My questions are :
- What power do I need ?
- What cheap amp and speakers can I buy ?
---
Some explanations :
I would like to move a giant mixture of non-newtonian fluid to make Faraday waves.
- This non-newtonian fluid is made of cornstarch and water (so, it is edible by children).
- Faraday waves are a very funny phenomenon. Here is a famous video about it ("fingers" start at 2:00) : http://www.youtube.com/watch?v=nq3ZjY0Uf-g
---
Every year, I build a machine for children. Last year, it was a vortex cannon called "boum".
(Examples : http://www.youtube.com/watch?v=lMLop6MIwUU)
If I succeed, the new machine will be called "life".
Thank you very much for your help !
Hi,
Amplitude < 1mm does not mean a lot because anything
can be moved a small amount by a small amount of energy.
There are bass shakers :
http://www.parts-express.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-028&ctab=1#Tabs
But these exploit efficiency around a resonance to
be effective which is why they are not widerange.
Doing 20Hz to 200Hz at whatever "g" is required is a different matter.
I'm assuming here you are not talking about 20Kg of mixture, it is
fairly obvious no cheap amplifier or speakers can move around 20kg,
given a typical 200mm subwoofer cone mass might be 20 grams.
For a resonant system, i.e. at a fixed frequency, e.g. 100Hz, it will
be a lot easier to build up the amplitude and the related "g" force
of the related acceleration, velocity and amplitude.
The higher the frequency the lower the amplitude you need.
If you do literally mean 20Kg of mixture ("giant") you also need
to specify your target g force and the frequency. Without a
resonant system at that frequency you will struggle.
Power requirements are difficult to estimate becuase it will
depend on system losses, not a direct brute force input.
/sreten.
Amplitude < 1mm does not mean a lot because anything
can be moved a small amount by a small amount of energy.
There are bass shakers :
http://www.parts-express.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-028&ctab=1#Tabs
But these exploit efficiency around a resonance to
be effective which is why they are not widerange.
Doing 20Hz to 200Hz at whatever "g" is required is a different matter.
I'm assuming here you are not talking about 20Kg of mixture, it is
fairly obvious no cheap amplifier or speakers can move around 20kg,
given a typical 200mm subwoofer cone mass might be 20 grams.
For a resonant system, i.e. at a fixed frequency, e.g. 100Hz, it will
be a lot easier to build up the amplitude and the related "g" force
of the related acceleration, velocity and amplitude.
The higher the frequency the lower the amplitude you need.
If you do literally mean 20Kg of mixture ("giant") you also need
to specify your target g force and the frequency. Without a
resonant system at that frequency you will struggle.
Power requirements are difficult to estimate becuase it will
depend on system losses, not a direct brute force input.
/sreten.If bass shakers don't work,
Google "shake table" and you'll find thousands of references and DIY articles.
Shake tables are used for physics demos. and more practically for testing the sturdiness of consumer products.
The low frequency and strength they provide may be what you are after.
Interesting project...
Syd
Google "shake table" and you'll find thousands of references and DIY articles.
Shake tables are used for physics demos. and more practically for testing the sturdiness of consumer products.
The low frequency and strength they provide may be what you are after.
Interesting project...
Syd
May I assume you had something like this in mind:
http://experiments.magnify.net/video/Fingers-and-Holes-in-a-Shaken-C
I have seen many physic demonstrations on line ( similar to this one ).
I am sure if you e-mailed them they would tell you how they set up their demos.
I noticed the mass they used was a fraction of what you requested. The demo can be performed with less mass.
Syd
http://experiments.magnify.net/video/Fingers-and-Holes-in-a-Shaken-C
I have seen many physic demonstrations on line ( similar to this one ).
I am sure if you e-mailed them they would tell you how they set up their demos.
I noticed the mass they used was a fraction of what you requested. The demo can be performed with less mass.
Syd
Thank you very much for your answers.
Sreten : I do try to move 20 kilos of fluid, not 20 grams. I would like to build a table big enough to have 5 or 6 people around, not a small laboratory plate.
This size causes 3 problems :
- The stability. The table has to stay horizontal, and move only vertically. If I have more than one support, they have to move in phase.
- The adjustment. I need to change frequency AND amplitude because the phenomenon is unstable. I didn't find any DIY shake table which allows the two parameters.
- The noise. This is just for comfort, but this is important. I think electro-magnets are more silent than a engine. That is why I tried to do with speakers.
As you notice, I dont know how to estimate Power requirements. Any ideas ?
---
Yes HK26147, I started with this video (In my first post, I give the youtube link). My calculations are based on their parameters :
At 2:00 on the video, I read : f=120Hz and a=25g.
If the movement of the table is : A(t)=A.sin(w.t)
Acceleration is : A''(t)=A.w^2.sin(w.t)
a=25g means : A.w^2=25
w=2.pi.f=750
so A = 25 / 750^2 = 4 E-5 m = 40 microns.
I hope I have the good parameters.
The problem is how to do it on large scale, in concrete terms...
Sreten : I do try to move 20 kilos of fluid, not 20 grams. I would like to build a table big enough to have 5 or 6 people around, not a small laboratory plate.
This size causes 3 problems :
- The stability. The table has to stay horizontal, and move only vertically. If I have more than one support, they have to move in phase.
- The adjustment. I need to change frequency AND amplitude because the phenomenon is unstable. I didn't find any DIY shake table which allows the two parameters.
- The noise. This is just for comfort, but this is important. I think electro-magnets are more silent than a engine. That is why I tried to do with speakers.
As you notice, I dont know how to estimate Power requirements. Any ideas ?
---
Yes HK26147, I started with this video (In my first post, I give the youtube link). My calculations are based on their parameters :
At 2:00 on the video, I read : f=120Hz and a=25g.
If the movement of the table is : A(t)=A.sin(w.t)
Acceleration is : A''(t)=A.w^2.sin(w.t)
a=25g means : A.w^2=25
w=2.pi.f=750
so A = 25 / 750^2 = 4 E-5 m = 40 microns.
I hope I have the good parameters.
The problem is how to do it on large scale, in concrete terms...
Hi,
I cannot estimate the power requirements except for the brute
force approach, which with 20kg is simply not going to work.
If you want variable frequency I'd say you have to make it
mechanically adjustable (e.g. number of springs) and also
make the electronics self oscillate at the natural frequency.
/sreten.
I cannot estimate the power requirements except for the brute
force approach, which with 20kg is simply not going to work.
If you want variable frequency I'd say you have to make it
mechanically adjustable (e.g. number of springs) and also
make the electronics self oscillate at the natural frequency.
/sreten.This is not a job for 4 speakers,
I suggest
http://www.dataphysics.com/products/shakerfamily/index.htm
http://www.dataphysics.com/products/shakerfamily/shakers/index.htm
I suggest
http://www.dataphysics.com/products/shakerfamily/index.htm
http://www.dataphysics.com/products/shakerfamily/shakers/index.htm
F=ma
m=20kg
a=25g
F=20*25*9.8=5000N
For a loudspeaker motor F=B*l*i
So for one speaker Bl=20 (some pro drivers - most drivers have Bl~10) you need 250 amperes. That's a big amplifier
You might wish to also calculate the SPL of whatever area of fluid you are thinking of moving at the excursion you are planning. Might be a fair amount of noise the larger the container gets...
The larger the container gets the more likely you will have modal resonances in the container that may or may not be interesting to watch...
m=20kg
a=25g
F=20*25*9.8=5000N
For a loudspeaker motor F=B*l*i
So for one speaker Bl=20 (some pro drivers - most drivers have Bl~10) you need 250 amperes. That's a big amplifier
You might wish to also calculate the SPL of whatever area of fluid you are thinking of moving at the excursion you are planning. Might be a fair amount of noise the larger the container gets...
The larger the container gets the more likely you will have modal resonances in the container that may or may not be interesting to watch...
Hi everybody,
Thank you very much for your answers and your help.
Since last week, I follow two ideas :
- I asked the price of a profesional shake table. There is a firm near my town and I hope they will call me back soon.
- One of my friend have a PA system. I will do some tests on it, just to have a order of magnitude. Maybe I will buy a cheap loudspeaker for my experiments.
Of course, I will give you a complete report !
once again, thank you very much for your help.
Thank you very much for your answers and your help.
Since last week, I follow two ideas :
- I asked the price of a profesional shake table. There is a firm near my town and I hope they will call me back soon.
- One of my friend have a PA system. I will do some tests on it, just to have a order of magnitude. Maybe I will buy a cheap loudspeaker for my experiments.
Of course, I will give you a complete report !
once again, thank you very much for your help.
Loudspeakers seem like an extremely inefficient way of moving that much mass.
Off the top of my head you could try using electric motors and shafts running under the table with little cams on them much like the way the inlet/outlet valves in a car engine are opened and closed. You may need springs in tension under the table to pull it back down fast enough at higher frequencies I'm not sure. Varying the frequency would be as simple as adjusting the voltage fed to the motor
Off the top of my head you could try using electric motors and shafts running under the table with little cams on them much like the way the inlet/outlet valves in a car engine are opened and closed. You may need springs in tension under the table to pull it back down fast enough at higher frequencies I'm not sure. Varying the frequency would be as simple as adjusting the voltage fed to the motor
Let's inject some numerical values into your problem:pianomambo said:
A typical speaker motor might have a force factor of 5N/A.
For continuous operation, it would not be reasonable to exceed 2.5A, even for a high power speaker. This translates into 12.5N.
If you use a push-pull arrangement (total of 8 speakers), you will get 100N.
If you upgrade to high performance units, you might double that value: 200N. If you need large excursions and a high frequency, you'll be on the weak side.
Other types of actuators might be better suited to your application, something like a hard disk head positionner f.e.
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